1. Technical Field
The subject invention is directed toward an increased efficiency valve system for a fluid pumping assembly wherein the suction and discharge ports in a valve plate have a specific configuration and disposition relative to one another to optimize the volumetric efficiency of a fluid pumping assembly.
2. Description of the Prior Art
Fluid pumping assemblies of the prior art, such as refrigerant compressors, typically employ reed valve systems for opening and closing intake and exhaust ports in the valve plate thereby controlling the ingress of refrigerant vapor from a suction chamber into a compression chamber under a predetermined lower pressure and the egress of the compressed vapor through the discharge port and into a discharge cavity at a predetermined elevated pressure.
More specifically, and with reference to the fragmented cross-sectional side view of FIG. 1, a portion of a prior art fluid pumping assembly is shown, generally at 10, and includes a cylinder block 12, a head 14 fixedly attached to the cylinder block 12 with a valve plate 16 disposed between the cylinder block 12 and head 14. The cylinder block 12 includes a cylinder insert 18 fixedly disposed therein and which defines a compression chamber 20. The head 14 includes a suction chamber 22 and a discharge chamber 24. The discharge chamber 24 is in fluid communication with the compression chamber 20 via an outlet port (not shown) when the one way discharge flapper valve 26 is moved to its open position. Discharge flapper valves 26 of the prior art generally work in conjunction with a back stop 28 which serves to limit the distance a discharge valve can flex in response to the elevated pressures developed in the compression chamber 20 during the compression stroke of a piston 27.
A suction chamber 22 is in fluid communication with the compression chamber 20 via an inlet port 30 when the one way inlet suction reed valve member 32 is moved to its open position. Suction reed valve members 32 are typically made of thin plates of spring steel and are designed to flex away from the inlet port under certain predetermined minimum pressures. However, in order to limit the amount of flex (and therefore stress) to which a reed valve member 32 is subjected and thereby increasing its working life, prior art valve systems employ thumb nails 34 which can be defined by shoulders presented in the compression chambers 22 by the cylinders 18. However, thumb nails 34 have become increasingly undesirable because an unacceptable level of noise is generated when the suction reed valve member 32 comes into abutting contact with the thumb nail 34 during the intake stroke of a piston 27.
Furthermore, one of the design objectives for fluid pumping assemblies is to increase the volumetric efficiency of the assembly. One way this can be achieved is by increasing the size of the inlet and outlet ports. However, such solutions are limited by the finite area of the valve plate subscribed by the cross section of the individual cylinders 18 and the stresses induced on the valve plate when more material is removed to enlarge the ports. There is only so much space in a valve plate within the limited confines of a cross section of the cylinder in which to position enlarged inlet and outlet ports while attempting to maintain the structural integrity of the valve plate. Optimum intake port size must be balanced with the fact that the thin metallic suction reed valves can be deformed into the inlet ports under the influence of the elevated pressures generated in the compression chambers during the piston compression stroke. Such deformation in the reed valves create "oil can" stresses in the suction reed valve which can reduce working life and lead to premature failure of the reed valve.
As such, it has always been a design objective to optimize volumetric flow efficiency while maintaining the structural integrity of the valve system. Prior art valve systems have attempted to do this with varying degrees of complexity and varying degrees of success.